Heavy snowfall in large parts of Europe has forced airlines to cancel large numbers of flights to London's Heathrow airport and the main airports in Paris.

Heathrow scrapped a fifth of flights overnight, while the Charles de Gaulle and Orly airports on the outskirts of Paris cancelled 40 per cent, mostly short-haul services.

Flagship carrier Air France said it had managed to go ahead with almost all of its long-haul flights and just over half of its short- and medium-haul journeys, with average delays of about one hour.

Some airports, including in Lille in northern France and in Beauvais, outside of Paris, were forced to close, forcing budget carrier Ryanair to divert several flights to other airports.

More than 120 Ryanair passengers heading from Oporto in Portugal to Lille were left stranded in the western city of Nantes.

Airport officials said they would be brought to their final destination by bus on Monday.

Heathrow, owned by Spain's Ferrovial, said the reduced schedule - amounting to around 250 fewer flights - would help it cope with the snowfall without making further cancellations.

London's smaller Stansted and Gatwick airports said they were operating as normal on Sunday morning but that delays and some flight cancellations were likely.

The British Met Office said snow was likely to continue into Monday (local time).

As much as eight centimetres was expected in south-east England on Sunday, it said.

On average, 1,300 flights leave Heathrow daily. The airport, Europe's busiest, operates at close to full capacity.

"Many airports have plenty of spare runway capacity so aircraft can be spaced out more during low visibility without causing delays and cancellations," a spokesperson for Heathrow, whose owners have campaigned hard for more capacity at the London hub, said.

"Because Heathrow operates at almost full capacity, there is simply no room to reschedule the delayed flights."

More than 400 flights were cancelled on Friday, while on Saturday 111 flights, most of them operated by British Airways, were cancelled and hundreds of passengers spent the night in Heathrow's terminals.

BA said there had been a knock-on effect because many of its planes were in the wrong place after Friday's snow.

Services by Air France-KLM, Ireland's Aer Lingus and Germany's Lufthansa have also been affected.